The X-ray CT apparatus is an apparatus which obtains a tomographic image (hereinafter, described as a reconstruction image) of an object by calculating an X-ray absorption coefficient from an X-ray transmission image (hereinafter, described as projection data) of the object scanned from a plurality of directions, and is widely used in the medical or non-destructive inspection field. Especially in the medical field, the spread of multi-slice X-ray CT apparatuses has been progressing in recent years. The multi-slice X-ray CT apparatus acquires a plurality of reconstruction images by collecting the two-dimensional radiation data by one-time X-ray irradiation using an X-ray detector in which a plurality of detection element columns, each of which includes a plurality of X-ray detection elements arrayed in a channel direction along the surface of a reconstruction image, are arrayed in a slice direction, which is perpendicular to the channel direction, along the body axial direction of the object (for example, refer to PTL 1).
Since the multi-slice X-ray CT apparatus has such a structure, it is possible to photograph a wide field of view in the slice direction by one-time X-ray irradiation. Accordingly, a desired range can be scanned in a short time. As a result, not only can a photographing time be shortened, but also moving organs, such as the heart, can be scanned while suppressing blurring caused by the movement.
The X-ray detector of the multi-slice X-ray CT apparatus has a structure in which a semiconductor substrate formed with photoelectric conversion elements is mounted on a scintillator substrate which converts an X-ray into light. There is a tiling technique for realizing a desired number of X-ray detectors by forming detector blocks, the number of which is smaller than a predetermined number of stages, and arraying the plurality of detector blocks in the slice direction from the constraints of the size of a semiconductor substrate used, the difficulty of manufacturing, and the cost (for example, refer to PTL 2 and PTL 3).